Tipping the ultrafast photochemical balance of cis-stilbene

Multi-state nonadiabatic molecular dynamics simulations combined with MRSF-TDDFT have revealed that the quantum yield of photoproducts in cis-stilbene is dependent on the initial temperature of the ground state, thereby resolving controversies regarding the competition between isomerization and ring-closure reactions. Specifically, 4,4-dihydrophenanthrene (DHP) is preferentially formed at low temperatures, while trans-stilbene is favored at high temperatures. The ethylenic torsional motions ( $\theta$ ) are particularly coupled with the initial thermal condition, tipping the balance of the competition.